Current antenna systems can be divided into three main categories: i) antennas which radiate with a fixed pattern and polarization (“standard antennas”); ii) antennas including a matrix of active elements that radiates with variable patterns and/or polarizations by conveniently phasing each active element (“phased array”); and iii) antennas including a single active element showing a different pattern and polarization depending on the adopted current distribution on the radiating element (“reconfigurable antennas”).
These two classes of adaptive antennas (phased arrays and reconfigurable antennas) have received strong attention in the last several years with respect to standard antennas due to their capability of dynamically changing the radiation properties of the antenna in response to the multivariate behavior of the wireless channel. The reconfigurable antenna solution is then preferable with respect to a phased array antenna mainly because i) it employs a single active element and therefore it occupies a small space and ii) it allows for high radiation efficiency since it does not employ phase shifters and power dividers.
Different types of reconfigurable antennas capable of changing pattern and polarization have been proposed in the art. These antennas may employ embedded switches or variable capacitors to change the current distribution on the metallization of the active element, or may employ an active antenna element surrounded by passive elements (parasitic elements) loaded with variable capacitors or connected to switches.
However, none of the prior art approaches allows radiating with omnidirectional and directional radiation patterns while preserving a planar design (e.g., two layer printed circuit board). To the inventors' knowledge, the only antenna technology capable of achieving this type of reconfigurability is the one described by M. Facco and D. Piazza, in “Reconfigurable Zero-Order Loop Antenna,” IEEE International Symposium on Antennas and Propagation and USNC/URSI, 2012. However, the metamaterial active element of such design along with the surrounded reactive components results in a narrow frequency bandwidth. The invention described herein allows designs of planar reconfigurable antennas capable of generating omnidirectional and directional radiation patterns over a wide frequency band or over multiple bands.